The present invention relates to a belt with several synthetic fiber strands which extend at a spacing and which are embedded in a belt casing. Belts of that kind are particularly suitable for use as support means or drive means in an elevator installation.
Running cables are an important, strongly loaded mechanical element in conveying technology, particularly in elevators, in crane construction and in mining. The loading of driven cables as used in, for example, elevator construction is particularly multi-layered.
In the case of conventional elevator installations the car frame of a car guided in an elevator shaft and a counterweight are connected together by way of several steel stranded cables. In order to raise and lower the car and the counterweight, the cables run over a drive pulley that is driven by a drive motor. The drive moment is imposed under friction couple on the respective cable portion contacting the drive pulley over the looping angle. In that case the cables experience tension, bending, compression and torsion stresses. Depending on the situation the stresses arising have a negative influence on the cable state. Due to the usually round cross-section of a steel stranded cable the cable can twist when running around pulleys and is thereby loaded in bending in the most diverse directions.
Apart from demands on strength, in the case of elevator installations there also exists for reasons of energy the requirement for smallest possible masses. High-strength synthetic fiber cables, for example of aromatic polyamides, particularly aramides, with intensely oriented molecular chains fulfil these requirements better than steel cables.
Cables made of aramide fibers have by comparison to conventional steel cables only a quarter to a fifth of the specific cable weight for the same cross-section and same load-carrying capability. By contrast to steel, however, aramide fiber has, due to the alignment of the molecular chains, a substantially lower transverse strength in relation to the longitudinal load-carrying capability.
In addition, these cables made of aramide fibers are subjected to twisting phenomena and bending loads which can lead to fatiguing or breakage of the cable.
Apart from the most diverse cables there are also belts which are used industrially. Belts are principally used by the automobile industry, for example as V-belts, or by the machine industry. Depending on the degree of loading, belts of that kind are steel-reinforced. In that case they are usually endless belts. Monitoring of an endless belt is relatively costly and for reasons of cost does not come into use in the automobile sector. The automobile industry has therefore followed the path of providing the belts that are used with a service life limitation in order to ensure that a belt is exchanged before it runs the risk of failure. Such a service life limitation is suitable only in the case of large batch numbers, since the necessary investigations can be made here, and in the case of belts which are simple to replace.
Elevator installations, in which cogged belts are used, are already described such as in, for example, the patent application with the title “Elevator with belt-like transmission means, particularly with a V-ribbed belt, as support means and/or drive means” of the same applicant as the present invention. A cogged belt is a mechanically positive, slip-free transmission means which, for example, circulates synchronously with a drive pulley. The load-carrying capability of the teeth of the cogged belt and the number of teeth disposed in engagement determines the load transfer capability.
In order to create a belt which is usable as an entirely adequate and above all reliable/support means or drive means it may have to be ensured that fatigue phenomena of the belt and, above all, incipient risk of breakage are recognizable.
A service life restriction, such as, for example, prescribed by the automobile industry, will be less suitable in the case of a belt which is to be used as a support belt or drive means for an elevator.
Other monitoring means which have proved satisfactory in the case of steel cables, such as optical monitoring, cannot be used in the case of belts since the strands of the belt are embedded in a belt casing and thus invisible. Further monitoring methods such as X-ray monitoring or ultrasound monitoring are uneconomic when a belt is used in the elevator system.